A large number of plastic bottles and similar plastic containers used today are manufactured in a stretch blow molding process. In this process, a so-called preform is first manufactured with a generally elongated, tube-like shape. This shape can have a bottom on one of its longitudinal ends. On the other end, it can have a neck section with an interlocking connection of a closure with a corresponding engagement. The interlocking connection of a closure can be, for example, threads formed on the outer surface of the neck piece or bayonet-like protrusions or recesses. The preform is inserted into a mold cavity of a blow mold and inflated using a medium, usually air, that is blown in via overpressure. Additionally, the preform is thereby axially elongated with a horizontal bar that is driven through the neck opening. After the stretching/blowing process, the finished plastic container is demolded out of the blow mold.
In the so-called one-step stretch blow molding process, the preform can be reshaped into a plastic container immediately following its manufacture in the injection-molding process, without intermediate cooling and storage. Plastic containers can be, however, generally manufactured in a two-step stretch blow molding process, in which the preforms are initially injection-molded, cooled, and stored for later use. The manufacture of the plastic containers takes place separately (both spatially and temporally) in a separate stretch blow molding process. In this later stretch blow molding process, the preforms can be heated again in order to make plastic bottles. In order to do this, for example, a desired temperature profile is set using infrared radiation over the axial and/or radial extent of the preform. This temperature profile enables the stretch blow molding process. After the preform is set into the molding tool, it is radially shaped using a gas that is blown in with overpressure and axially stretched using a stretching rod. Afterwards, the finished plastic container is demolded.
In the production of mass-produced items (like, for example, plastic bottles made of polyethylene terephthalate, or PET), material usage represents a factor for competitiveness and environmental balance. Due to the very high quantities in which plastic bottles are manufactured, reductions of the material weight on the order of tenths of a gram can very quickly lead to material saving on the order of tons. As a result, great efforts were taken in the past to reduce the material weight of the preforms for plastic bottles, especially PET bottles. With the preforms known from the prior art, it was believed that the optimum had been reached. The plastic bottles manufactured from the preforms are manufactured to meet the required mechanical strengths, temperature stabilities, and gas barrier characteristics. The efforts to reduce the material weight were disadvantageous in that they required multiple modifications of the stretch blow molding devices and the bottling plants. This is, from the standpoint of the stretch blow molding device operator as well as from the standpoint of the bottler of plastic containers made from the preform, an extremely unsatisfactory state of affairs.
Preforms known from the prior art can have, in the neck section, minimum wall thicknesses of 0.9 mm to 2 mm. These wall thicknesses are used to impart to the neck section, which is not further strain-hardened during the stretch blow molding process, the mechanical strength, the gas-tightness, and the internal stress resistance necessary for the reception of the closure, even at raised outside temperatures. Consequently, the neck section of the preform makes a not-insignificant contribution to the overall weight (and therefore to the material usage of the preforms).